1. Field of the Invention
This invention relates to an apparatus for creating a gaseous discharge and more particularly, to gaseous discharge for use as a laser amplifier section.
2. Description of Prior Art
U.S. Pat. No. 4,755,999 titled, "Laser Apparatus Utilizing a Magnetically Enhanced Electrical Discharge" (July 1988, J. A. Macken) describes a laser amplification section of a laser apparatus in which a discharge is spread to form a thin sheet or an annular shape. Lasers with these discharge shapes, have subsequently become known as "slab lasers" and the discharge as a "slab discharge." The term "slab" is technically not grammatically correct but this common usage will be utilized here. In this laser apparatus, a gaseous filled cavity is bounded by a first and second opposing surfaces. These are closely spaced relative to the dimensions of the surfaces. Elongated electrodes within the cavity generate a discharge. Magnets generate a magnetic field within the cavity. This magnetic field is oriented generally perpendicular to the opposing surfaces. The discharge is relatively narrow in the dimension parallel to the magnetic field compared to the dimension perpendicular to both the magnetic field and the electric field. The magnetic field exerts a force on the discharge. When the magnetic field exceeds a threshold value, the discharge is homogeneous within the cavity. This homogeneous discharge condition is well suited for exciting gaseous lasers such as CO.sub.2 lasers. Heat generated by this discharge is efficiently removed by thermal conduction to the two opposing surfaces. The surfaces, in turn, are liquid-cooled.
The discharge as described in this patent can have some disadvantages. First, it is sometimes necessary to use multiple electrodes. Each of these electrodes has some form of ballasting to help distribute the discharge. Second, the strength of the magnetic field must be above a threshold number which in thin cavities, can be high. Third, the discharge can take up to 0.1 seconds to become stable when the power is first applied to the electrodes. This time is too slow to permit modulation of the laser by modulating the discharge.
The invention described herein is an improvement whereby a small amount of AC electrical power applied perpendicular to the opposing surfaces can assist the magnetic field in stabilizing the discharge. This can reduce the threshold magnetic field required for stability. It also can decrease the need for multiple electrodes. Finally, the initiation of the discharge can occur more rapidly when the transverse AC field is present.